Cobra 29 classic shows antenna error light when Installed in CB "cubby" of Freightliner M2

If its similar to mine there isn't much space at all, as a matter of fact the power cord looks to be tight up against what i think is 1 of the mounting studs for the cab clearance lights.
I have ran into several guys with higher powered radios that just for some reason do not like being in the upper compartment, they start out there then a couple of days later there mounting under neath upper compartment.

 

Try one of these,

 

I have the same problem with mine but my radio is in a T880 Kenworth. If I put my radio in my old (2017 Kenworth T880) it works fine no warning light, but when I put it in my 2021 Kenworth T880 the antenna warning light comes on and my screen is above 3 in the 2021 but is 1.3 in the 2017